The purpose of this study is to investigate the feasibility of combining heavy-slow resistance training with an ultrasound-guided corticosteroid injection to reduce pain in individuals with plantar fasciopathy. Feasibility will be evaluated using the acceptability of the combined interventions and exercise compliance.

After eligibility has been confirmed, participants are instructed in performing the exercise which will be heel raises. Participants will be asked to complete the exercise standing with the forefoot on a step. The toes are maximally extended by placing a towel underneath them. The participant is instructed to perform a heel raise to maximal plantar flexion in the ankle joint and afterwards to lower the heel to maximal dorsiflexion. Supporting oneself for balance by touching the hands on a wall or a rail is allowed. The participants are instructed in performing the exercise with a load as heavy as possible but no higher than 8RM and for as many sets as possible. If the participants feel they can perform more repetitions than their load corresponds to (e.g. 10 repetitions when the load is supposed to be 8RM) an external load consisting of a backpack with books or water bottles to add weight will be used. Participants are asked to start performing the exercise as soon as they feel ready but not before 24 hours after the injection.

Participants will receive patient education on what is known about the condition in terms of risk factors and aetiology, the pathology, activity modification, and the rationale for why the combination of heavy slow resistance training and an US-guided corticosteroid injection could lead to recovery. They will be told that compliance to the exercise programme is very important and that compliance to the exercises is associated with their recovery. They are also informed about other types of evidence-based treatments however, they are asked to refrain from seeking other treatments during the course of the study. A silicone heel cup will be given to all participants and they are asked to use the heel cup as much as possible. If the participant already uses an insole or any other type of foot orthosis they will be allowed to continue wearing this if they do not want to use the heel cup. Participants are asked not to progress the method used to achieve 8RM when they start to do the exercise after the injection until Week 3 of the exercise program. If standing on both feet was sufficient to achieve 8RM at baseline, the participant must not perform the exercise single-legged after the injection regardless of any pain reduction afforded by the injection.

Participants receive an ultrasound-guided corticosteroid injection between 5 and 8 days after baseline. A 21-gauge, 40 mm needle is connected to a 2.5 cm3 syringe filled with 1 ml Triamcinolonhexacetonid (Lederspan, Meda) + 1 ml Lidocain 10 mg7ml (Xylocain, AstraZeneca). The skin is cleansed with Chlorhexidine alcohol 0.5 % (Medic). The needle is inserted with a medial approach under ultrasound-guidance aligned to the long axis of the ultrasound transducer. The injection is placed anterior to the plantar fascia insertion on the calcaneal bone in the region of maximal fascia thickness. If participants are not categorised as improved based on the Global Rating of Change after the 8 weeks of exercise they will be offered to receive a second injection and are advised to continue performing the exercise. These participants will have an additional follow-up 8 weeks after the second injection.

All statistical analyses will be performed according to a pre-established analysis plan. STATA ver. 14 will be used as statistical software.

Feasibility outcomes To conclude that the combined interventions are feasible the following three criteria will need to be met: i) ≥10/20 rate the combined interventions as "acceptable". The rationale for choosing this criterion is that the effect of the combined interventions has yet to be established and effective treatment could justify the use of an intervention that is slightly uncomfortable or considered slightly unacceptable by patients (e.g. chemo therapy is a very uncomfortable treatment but is tolerated and accepted by patients because of the potential effective outcome). Any dropouts after the injection will be dichotomized as "unacceptable". ii) based on the self-reported training diaries ≥15/20 participants will need to have performed ≥20/27 possible training sessions; and iii) ≥15/20 participants will need to have started performing the exercise ≤7 days after the injection. Weekly recruitment rate will be reported using descriptive statistics.

Explorative quantitative outcomes Any changes in FHSQ, IPAQ, and PSEQ will be examined using a one-way repeated measures ANOVA, with time (baseline assessment, 4 weeks, or 8 weeks) as the independent factor, and FHSQ, IPAQ or PSEQ, respectively, as the dependent variable. Changes in plantar fascia thickness from baseline assessment to the 8-week follow-up and the difference in mean daily heel pain from before to after the injection will be examined using paired t-tests. GROC will be reported using descriptive statistics.

If any participant decides to drop out before having received the injection a new participant will be recruited.

Inclusion Criteria:

• History of inferior heel pain for at least three months before enrolment
• Pain on palpation of the medial calcaneal tubercle or the proximal plantar fascia
• Thickness of the plantar fascia of 4 mm or greater
• Mean heel pain of 30 mm or above on a 0 to 100 mm VAS during the previous week

Exclusion Criteria:

• Below 18 years of age
• History of inflammatory systemic diseases
• Prior heel surgery
• Pregnancy
• Pain or stiffness in the 1st metatarsophalangeal joint to an extent where the exercises cannot be performed
• Corticosteroid injection for plantar fasciopathy within the previous six months
• Known hypersensitivity to corticosteroids or local anaesthetics
• Skin or soft tissue infection near the injection site